Rotating biological contactors commonly comprise a cylindrical structure with a labyrinthine interior designed to provide extensive air/water contact surfaces. The cylinder rotates about a horizontal axis in a secondary wastewater treatment tank. Rotating biological contactors provide surfaces for the growth of biomass which has the ability to absorb, adsorb, coagulate, and oxidize organic constituents of the wastewater.
Wastewater treatment facilities have included rotating biological contactors (RBC's) supported in treatment tanks and rotated partially submerged in wastewater in the treatment tanks so that the surfaces of the contactor are alternately exposed to the wastewater and to oxygen in the overlying atmosphere. A film of wastewater is carried into the air and trickles down the surfaces of the contactor while absorbing oxygen from the air. Organisms in the biomass remove dissolved oxygen and organic materials from the film of wastewater and unused dissolved oxygen in the wastewater film is mixed with the contents of wastewater in the tank.
Anaerobic reactors of wastewater treatment facilities have also included RBC's in treatment tanks. The RBC's of the anaerobic reactors are completely submerged in wastewater and provide denitrification of wastewater in the tank.
Rotating biological contactors can be driven by a motor, or by air as disclosed in U.S. Pat. No. 4,668,387, issued to Davie et al. on May 26, 1987 and incorporated herein by reference or as disclosed in U.S. Pat. No. 3,886,074, issued to Prosser on May 27, 1975 and incorporated herein by reference. In an air drive system, air is released below an RBC via an air header, and rises into air cups provided around the outer perimeter of the RBC. The captured air exerts a buoyant force which exerts a torque on the RBC and shaft sufficient for rotation.